In manufacturing integrated circuit devices, it is important that the devices are defect free at the time of production, and reliable throughout their use. When defects are found in completed integrated circuit devices, the percentage of usable devices decreases, and the profitability of the manufacturer suffers, either through waste or required reworking. More importantly, when a semiconductor device fails after being installed, such a failure may cause an entire consumer electronics device to fail. That is, the failure of a single integrated circuit device may render an entire consumer electronics device unusable. Accordingly, it is important that manufacturers minimize defects in integrated circuit devices whenever possible.
One common source of failures in integrated circuit devices is found where components are soldered to contact pads, such as solder bumps of a flip chip ball grid array (BGA). A ball grid array is an advanced integrated circuit package comprising a substrate having contacts on the bottom for soldering the integrated circuit package to a circuit board. A wire bond BGA comprises a die having contact pads which are bonded to a contact pads on the surface of the substrate by way of wire bonds. In contrast, a flip chip BGA comprises a die having contact pads which are directly bonded to the substrate using solder bumps. Unlike in a wire bond BGA, the die having solder bumps is flipped over and placed face down in a flip chip BGA, with the conductive bumps connecting directly to corresponding contact pads on the top surface of the substrate. Many components of integrated circuit package are soldered to contact pads using solder balls which are reflowed when the component is placed. For example, a flip chip having contact pads is soldered to a substrate by reflowing a plurality of solder balls on the contact pads of the flip chip. One common cause of failures in soldering a flip chip to a substrate of an integrated circuit package may result from variations in the shape of the package. For example, warping of the package during the processing steps may lead to height variations between the contact pads on the flip chip die and contact pads of the substrate. Such warpage may cause weaker solder bonds where the height difference is excessive or where movement occurs as a result of warping during the reflowing process.
Variations in the integrated circuit package, other than warping, may also be introduced during the assembly of the integrated circuit package, such as the application of underfill or during lid attachment. Efforts are currently being made to reduce the warpage of the parts by changing materials used in the integrated circuit package. While these efforts may help reduce warpage, conventional devices continue to have defects, particularly as die sizes in flip chip packages increase. Further, some efforts to reduce warpage have reliability trade-offs. For example, by reducing the stresses in the underfill material to reduce warpage, the solder bumps themselves become exposed to additional stresses.
There have also been efforts to reduce the core thickness of a substrate to reduce the cost of the substrate and increase the electrical performance. However, a thin substrate warps easily during the assembly process when thermal stress is generated in the die due to different thermal coefficients of the substrate and die. Package warpage may often occur during package assembly process including lid attachment and ball placement due to the different thermal coefficients. As a result of various thermal stresses during the assembly process, a non-wet solder bump may be formed, which may result in an electrical open in the final product.
Accordingly, there is a need for an improved integrated circuit package and an apparatus for and method of assembling an integrated circuit package.